Full text
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| Author(s): |
Alejandra Matiz López
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB) |
| Defense date: | 2013-02-21 |
| Examining board members: |
Helenice Mercier;
Marcos Pereira Marinho Aidar;
Halley Caixeta de Oliveira
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| Advisor: | Helenice Mercier |
| Abstract | |
Urease is a very important enzyme in the hydrolysis of urea, providing nitrogen to the plant. Previous studies developed in our Laboratory-IBUSP showed the preference of the epiphytic tank-bromeliad, Vriesea gigantea, for urea as a nitrogen source, and the localization of urease in the plasma membranes and cytoplasm of leaf cells. Recent evidences obtained also in our laboratory suggested a possible use of the CO2 generated by hydrolysis of urea. Even with these results, it is not known yet if in a water shortage situation the plant would possess an even higher preference for urea (reflected by an increase of urease activity), as in this situation the stomata are closed and the influx of atmospheric CO2 into the plant is limited. The analyses were made in three different leaf portions: apex, middle and basal. With the aim of characterizing the photosynthetic state of the leaf, was measured the relative water content, nocturnal organic acid storage, and enzymatic activities of phosphoenolpyruvate carboxylase (PEPC) and malate dehydrogenase (MDH). In addition, after 8 days of drought (by exposure to a solution containing 30% of polyethylene glycol - PEG), the detached leaves were treated with urea, and the urease activity and CO2 accumulation by cytolocalization were measured. The apical portion showed a significant increase of PEPC activity and nocturnal storage of citrate and malate, indicating that the apical portion is capable of increasing Crassulacean acid metabolism (CAM) expression under water shortage. In addition, in the apical portion of leaves kept in PEG and urea showed higher urease activities and CO2 accumulation at night than the control. CO2 buildup from urea hydrolysis was observed next to the chloroplasts and wall cells. Once in a limited CO2 situation to the plant, as is that case of water shortage, the results presented in this survey suggest that urea would be a highly important nitrogen source in the ecophysiology of plants. Therefore, besides urea being a nitrogen source, it could also be a source of carbon at least for epiphytic tank-bromeliads (AU) | |
| FAPESP's process: | 10/13836-1 - Urea utilization in Vriesea gigantea (Bromeliaceae) leaves under water shortage, much more than a nitrogen source |
| Grantee: | Alejandra Matiz Lopez |
| Support Opportunities: | Scholarships in Brazil - Master |